The present invention relates to a friction welding apparatus for friction welding a pair of work pieces together by pressing one of the work pieces against the other while rotating the work pieces relatively.
Various types of friction welding apparatuses are known, one of which is disclosed by Japanese Patent Application Publication No. 2001-113379. The friction welding apparatus of this first publication includes a first holder for holding a first work piece, a second holder for holding a second work piece and a spindle motor for rotating the first work piece on its axis. A pair of hydraulic cylinders or a pair of ball screws is provided for moving the second holder toward the first holder. Another friction welding apparatus is disclosed by Japanese Patent Application Publication No. 56-102390. The friction welding apparatus of this second publication includes a frame, a spindle stock mounted slidably to the frame and holding a first work piece, and a spindle motor for rotating the first work piece on its axis. The frame has an externally threaded member inserted in the spindle stock, an internally threaded member engaged with the externally threaded member, and a thrust motor for rotating the internally threaded member. When the internally threaded member is rotated, the first work piece is moved by the spindle stock toward a second work piece and then in pressing contact with the second work piece for friction welding the work pieces together.
Though the first publication discloses the use of hydraulic cylinders in the friction welding apparatus, it fails to disclose an apparatus using any specific ball screw. In addition, the second publication discloses a structure for sliding the spindle stock by rotating the internally threaded member, but it is of a portable type. For application of the structure of this portable friction welding apparatus to a stationary type friction welding apparatus, it is necessary to provide any additional means for rotatably holding the internally threaded member at its outer periphery. However, the provision of such additional holder will inevitably result in an increased size of the apparatus. Therefore, the present invention is directed to a friction welding apparatus which can be made compact and has a reasonable structure.